Stabilization of peracids



ees,

STABRIZATION F PERACIDS Jesse T. Dunn, Charleston, and Donald L.Heywood, South Charleston, W. Va, assignors to Union CarbideCorporation, a corporation of New York No Drawing. Original applicationAug. 25, 1958, Ser. No. 757,089, new Patent No. 2,953,572, dated Sept.20, 1960. Divided and this application June 16, 1%0, Ser.

5 Claims. (Cl. 260-502) lgrivatives have-found use in the stabilizationof peracids and hydrogen peroxide. Nicotinic acid l-oxide, for example,has been prepared by peroxidation of nicotinic acid with hydrogenperoxide and acetic acid. Also by the oxidation-of an alkylpyridinel-oxide, such as 4-nitro-3- methylpyridine l-oxide, a good yield of the4-.nitronicotinic acid l-oxide'can be obtained. Several other methodsare known whereby the pyridinemonocarboxylic acid l-oxides can beobtained in good yields.

While the known methods for synthesizing the pyridinemonocarboxylic acidl-oXides gave good results, when such methods were used in an attempt toprepare the pyridinepolycarboxylic acid l-oxides, no reaction occurred,and the starting pyridinepolycarboxylic acids were quantitativelyrecovered. Despite the amount of work done on pyridine l-oxides, none ofthe pyridinepolycarboxylic acid l-oxides have been reported in theliterature. 7 While not wishing to be bound by the particular mechanismwhich favors the formation of pyridinepolycarboxylic acids rather thanthe corresponding l-oxide, a consideration of the possible factors willaid in understanding the present invention. It is known that oxidationof a nucleophilic functional group by peracids involves an electrophilicattack by the peracid on the electron-rich functional group, whether itbe a double-bond, nitrogen atom, sulfur atom, or the like. Any factorthat causes a decrease of the electron density at the nucleophiliccenter of the compound being oxidized results in a much slower rate ofoxidation. A second factor which greatly influences the rate of reactionof oxidation is the well-known phenomenon of steric hindrance which, dueto the physical structure of adjacent groups, shields or blocks thereactive center.

Both factors, the diminution of electron density at the electron-richcenter and steric hindrance, are believed to be operative in causing thepyridinepolycarboxylic acids to be unreactive towards l-oxide formation.The net efiect is withdrawal of electrons from the pyridine ring leavingan electron-deficient nitrogen atom. Additionally, where the carboxygroup is in the alpha position to the nitrogen atom, the well-knownzwitterion effect can exist where the nitrogen and oxygen of the acidgroup are bridged through hydrogen bonding.

It would thus appear that due to a combination of several factors, thepyridinepolycarboxylic acids are resistant to oxidation to thecorresponding l-oxides. It is therefore an object of the presentinvention to provide a new series of new pyridinepolycarboxylic acidsl-oxides and a method for their preparation whereby these compounds areprepared in good yield. A further object of the present invention is toprovide pyridinepolycarboxylic acid l-oxides which are useful asstabilizers.

Another object is to provide pyridinepolyca'rboxylic acid l-oxides whichare useful in the preparation of polyester condensation resins.

Other objects and a fuller understanding of the invention will be had byreferring to the following description and claims.

According to the present invention, a series of new pyridine l-oxidesare prepared by a special oxidation technique where such compounds couldnot be prepared by the usual peroxidation methods.

The compounds of this invention may be illustrated by the followinggeneral formula:

(R) i-n wherein (n) is a whole positive integer of from 2 to 4 and R isa member selected from the group consisting of hydrogen, lower alkyl,and nitro groups.

Representative of the compounds of the invention are2,3-pyridinedicarboxylic acid l-oxide, 2,4-pyridinedicarboxylic acidl-oxide, 2,5-pyridinedicarboxylic acid 1-ox ide,2,6-pyridinedicarboxylic acid l-oxide, cinchomeronic acid l-oxide,3,5-pyridinedicarboxylic acid l-oxide, 2,4,6- pyridinetricarboxylic acidloxide, 2,3,6-pyridinetricarboxylic acid l-oxide,2,3,5,6-pyridinetetracarboxylic acid l-oxide,4-methyl-2,6-pyridinedicarboxylic acid l-oxide,4-nitro-2,6-pyridinedicarboxylic acid 1-oxide, and the like.

It was found that all of the factors which were discussed above andwhich prevented the peroxidation technique from being used to preparethe pyridinepolycarboxylic acid l-oxides from the correspondingpyridinepolycarboxylic acids were entirely removed or greatly reduced ifthe acids were reacted in the form of the metal salt. By employing, forexample, the disodium, dipotassium or other salt, the resonance effectis probably reversed, since What was an electron withdrawing group(-ii-OH) is now a negative group -ii-o which actually repels electrons,thus maintaining or increasing the electronic density at the nitrogenatom. The steric effect is also reduced by the mutual repulsion of thenegative carboxy groups, and lastly, hydrogen bonding to give thezwitterion formation is not possible.

In the practice of this invention, in order to oxidize the polysodiumsalt of the pyrindinepolycarboxylic acid, the acid is taken up insolution and a known amount of aqueous or alcoholic sodium hydroxide isadded. Since peracids decompose rapidly in the presence of a trong base,an excess of alkali is avoided. Excess of oxidizing agent (peracid) isthen added and, after warming the solution for several hours, it iscooled, acidified and the pyridine l-oxide compound separated. 1

In the preferred practice of this invention, the pyridinepolycarboxylicacid. l-oxide to be oxidized is dissolved in a solution of sodiumhydroxide of aconcentration of from about 5 to about 20 percent byweight. Other alkali hydroxides can be used either in water or othersuitable solvent. An excess of peracetic acid in acetic acid or othersuitable solvent is then added dropwise, the mixture being maintained at50 C. While other peracids may be used, such as performic, perbenzoicand the like, peracetic is preferred. The molar ratio of peracid to thepyridinepolycarboxylic acid is not necessarily critical and can bevaried from about 1.25 to about 5.0, although the molar ratios above andbelow the aforesaid range can be employed if desired. Reactiontemperatures of from about 30 C. to about 100 C. may be used.

During the addition of the peroxidant, additional sodium hydroxidesolution is added simultaneously and in an amount sufiicient to maintaincomplete solution and yet avoid taking the solution to alkalinity.Finally, the solution is warmed on a steam bath for from about 1 to 3hours, cooled to room temperature and the pH adjusted to less than 1with a concentrated acid such as hydrochlon'c. The product is washed,dried and can be recrystallized from aqueous alcohol.

The products of this invention are useful as chemical intermediates,stabilizers for peracid solutions or as monomers for the preparation ofcondensation resins. For example, a pyridinedicarboxylic acid l-oxidecan condense with an alkanediol to give a polyester resin. When used asinhibitors for the peracids all that is required is an inhibiting amountsuificient to inhibit the peracid from decomposition. Concentrations offrom about 0.01 percent to about 1 percent by weight are preferred.

Preparation of the pyridinepolycarboxylic acids, the starting materialsof this invention, can be efiected by methods known to the art. Forexample, isocinchomeronic acid can be synthesized by oxidation ofZ-methyl-S- ethylpyridine with nitric acid.

The following examples are given by way of illustration of the presentinvention.

EXAMPLE I 2,5-Pyridinedicarbxylic Acid I-Oxide 2,5 pyridinedicarboxylicacid monohydrate (15.0 grams, 0.275 mole) was dissolved in 90 grams of10 percent aqueous sodium hydroxide and 45 grams of water. To thissolution was added 25 grams of a solution of 45 percent peracetic acidin acetic acid, concurrently with 20 grams additional 10 percent aqueoussodium hydroxide. The reaction was stirred vigorously during this time(20 ruins), and temperature was 40 C. After stirring for 1 hour more, 16additional grams of peracetic acid were added, and the mixture heatedfor 1 hour on the steam bath. After cooling, the solution was acidifiedwith cone. HCl, filtered, and the product washed with cold water anddried. Yield of 2,5-pyridinedicarboxylic acid l-oxide was 14 grams (86percent) of light tan crystals, M.P. 241244 C. A mixed melting pointwith 2,5-pyridinedicarboxylic acid showed a marked depression: 216218 C.Analysis.-Calcd. for C H O N: Acid equivalent, 91.5; percent C, 45.9;percent H, 2.73; percent N, 7.65. Found: Acid equivalent, 91.9; percentC, 46.1; percent H, 3.2; percent N, 7.73.

A sample of this product was decarboxyl-ated by heating in ethyleneglycol at 150 C. for 30 mins. to give nicotinic acid l-oxide, M.P. afterrecrystallization from methanol, 246-248 C. d. (uncorr.). Mixed M.P.s ofthis nicotinic acid l-oxide with nicotinic acid (M.P. 234 C.) and2,5-pyn'dinedicarboxylic acid l-oxide (above) showed marked depressions(199-208 C. and 187-230" C., respectively). Acid equivalent: Calcd. forC H O N, 139; found 143.

EXAMPLE II 2,6-Pyridinedicarboxylic Acid J-Oxide2,6-pyridinedicarboxylic acid (5.01 grams, 0.03 mole) was dissolved in30 grams 10 percent aqueous sodium hydroxide and grams water. To thiswas added 10 grams of a solution of 45 percent paracetic acid in aceticacid concurrently with 20 grams additional sodium hydroxide solution.After heating at 60 C. for 1 hour, an additional 5 grams peracetic acidsolution was added and the mixture was warmed on steam for an additionalhour. After cooling and acidifying with cone. HCl, the product wasfiltered to give 4 grams (73 percent) 2,6-pyridinedicarboxylic l-oxideas a white, crystalline product, M.P. 155-157 C. A mixed M.P. with2,6-pyridinedicarboxylic acid was depressed (151 C.), and a mixed M.P.with picolinic acid l-oxide (M.P. 157-159 C.) was also depressed (116C.). Analysis.-Calcd. for C H O N: Acid equivalent, 91.5; percent C,45.9; percent H, 2.73; percent N, 7.65. Found: Acid equivalent, 93;percent C, 45.54; percent H, 3.06; percent N, 7.94.

A sample of this 2,6-pyridinedicarboxylic acid l-oxide wasdecarboxylated by heating at 148-163 C. for 4 minutes, and the resultantproduct recrystallized from methanol to give picolinic acid l-oxide,M.P. and mixed M.P. with authentic picolinic acid l-oxide, 153154 C.

EXAMPLE III Stabilization 0 Peracetic Acid Solution With2,6-Pyridinedicarboxylic Acid I-Oxide Samples of peracetic acid in ethylacetate (initial conc. 43.7%) were heated at C. in glass vessels.Periodic titrations for peracetic acid gave the following percent byweight of peracetic acid at the time indicated.

Solution with 0.1% Control 2,6-Pyridinedi- (no inhibitor) carboxylicacid Time, l-oxide added hrs.

#1, #2, #1, #2, percent percent percent percent What is claimed is:

1. A process of inhibiting a peracid from decomposition which comprisesadmixing with said peracid an inhibiting amount sutficent to inhibitsaid peracid from decomposition of a compound of the formula:

wherein (n) is a whole positive integer of from 2 to 4 and R is selectedfrom the group consisting of hydrogen, lower alkyl, and nitro groups.

2. A process of inhibiting a peracid from decomposi tion which comprisesadmixing with said peracid from about 0.01 to about 1 percent by weightof a compound of the formula:

0 (E-OHM wherein (n) is a whole positive integer of from 2 to 4 and R isselected from the group consisting of hydrogen, lower alkyl, and nitrogroups.

3. A process of inhibiting peracetic acid from decom- 5 position whichcomprises admixing with said peracetic and R is selected from the groupconsisting of hydrogen, acid from about 0.01 to about 1 percent byweight of 2,6- lower alkyl, and nitro groups.

pyridinedicarboxylic acid l-oxide. 5. A composition of matter comprisingperacetic acid 4. A composition of matter comprising a peracid and andan inhibiting amount of 2,6-pyridinedicarboxylic acid an inhibitingamount of a compound of the formula: 5 l-oxide.

0 I; OH References Cited in the file of this patent UNITED STATESPATENTS (mm 10 2,609,391 Greenspan et a1. Sept. 2, 1952 Ny OTHERREFERENCES L Diels et al.: Chem. Abs, vol. 27, 1933, page 5329*.

Costa et aL: Chem. Abs, vol. 51, 1957, page 4823b. wherein (n) is awhole positive integer of from 2 to 4 (Above publications in PatentOffice Scientific Library.)

1. A PROCESS OF INHIBITING A PERACID FROM DECOMPOSITION WHICH COMPRISESADMIXING WITH SAID PERACID AN INHIBITING AMOUNT SUFFICENT TO INHIBITSAID PERACID FROM DECOMPOSITION OF A COMPOUND OF THE FORMULA: